Most telephone service subscribers recognize that a ringing telephone indicates an incoming telephone call. In many cases, the telephone station rings in response to the receipt of a ring signal. For example, a telephone company providing Plain Old Telephony Service (POTS) may receive a call for a given subscriber and may initiate the sending of a ring signal from a central office to the home of that subscriber. A common technique involves feeding a 75 Volt, 20 Hz Alternating Current ringing current down one wire of a twisted pair telephone line. The power supporting these signals comes from a large amount of batteries located in a central office of the service provider.
In addition, a service provider often relies on central office power to detect an off-hook condition at a customer premises. The off-hook condition will typically complete a circuit and “tell” a switch in the central office to send a dial tone to the premises. As mentioned above, the ring voltage and dial tone typically originate at the central office of a service provider. These signals in combination with the in-wall wiring of a subscriber's home facilitate wireline telephone services. A subscriber simply plugs a telephone station into an RJ-11 jack—connecting the telephone station to the in-wall wiring—and the subscriber can make and receive wireline telephone calls.
While this conventional version of wireline telephone service represents a nice option for some subscribers, these services have several shortcomings.